1. Field of the Invention
The present invention relates to a flow soldering apparatus, and more particularly to a flow soldering apparatus by which a substrate mounted with electronic circuit parts is contacted to a solder flow to solder the electronic circuit parts to the substrate.
2. Related Art
A flow soldering apparatus is used to solder electronic circuit parts to a circuit substrate such as a printed circuit board on which the electronic circuit parts are mounted. This flow soldering apparatus grips both side ends of the substrate firmly, transfers the same to a flow solder barrel and contacts the same to the solder flow for soldering by a robot arm as disclosed in JP-A-7-288380.
The substrate undergoes thermal expansion when it is contacted with the molten solder in the solder barrel. The substrate bows, because it is clamped at its both side ends. Thus, the quality of the soldering of the circuit parts on the substrate is lessened, and the resulting substrate will have a deformation.
Further, the molten solder in the solder barrel is oxidized when exposed in the air. Thus, an oxide film (oxides) is formed on the surface of the molten solder. When the substrate is transferred over the solder barrel in contact with the molten solder, the oxide film contacts the substrate and lessens the quality of the soldering. JP-U-58-119962 discloses a substrate holder unit having three peripheral walls. The walls hold the substrate and removes the oxide film. However, the walls tend to cause a space between the substrate and the molten solder right behind the front wall, because the substrate is held above the bottom end of the walls. As a result, unsoldered parts are likely to occur on the substrate, thus lessening the quality of the soldering.
The above JP-A-7-288380 proposes to rotate the substrate so that the soldering is effected from different directions. In this soldering operation, it is likely to occur that the molten solder jumps onto the upper surface of the substrate which should not be soldered.